In the prior art, there are many known magnetic particles which are used, for example, for removal of biological substances by absorption (e.g. EP 1 232 502 B1). In particular, particles in the nanometer range or micrometer range are used (DE 196 14 136 A1). Such particles are also used in DE 199 40 220 A1 in cancer treatment for selective magnetic heating.
In addition, the coating of pigments in a sol-gel process is known from DE 195 20 964 A1.
A further important use of composite materials is use as proppants. These are filler materials for hydraulically generated fissures in underground formations, the filling of which with hard spherical granules generates a stable region with high permeability for liquids, for example mineral oil.
The problem addressed by the invention is that of providing magnetic composite particles which enable achievement of controlled heating by application of an alternating field.